Fractionation process



Patented May 13, 1952 2,596,344 FRACTIONATION rnoosss Herbert A. Newey,

Richmond, and Edward C. Shokal and Theodore F. Bradley,

Oakland,

Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware N Drawing. Application August '21, 1948, Serial No. 45,564

17 Claims. 8 l

This invention is concerned with a new process for fractionating mixtures of certain polar organic compounds. Specifically, it is concerned with the fractionation of such mixtures as 'vegetable oil acids or their derivatives. The fractionation of naturally-occurring mixtures of organic materials is necessary for their application in specific industries. For example, use of vegetable oils and the like in coating compositions requires removal of the less suitable components, which in most cases are the relatively saturated species. l-leretofore, fractionation of vegetable oils has been eiiected by such means as fractional distillation or fractional crystallization, either of which methods. may be combined with solvent extraction. Alternatively, the latter process alone has been used. These previously known processes vary considerably in their relative efficiency and especially in economy.

It is an object of the present invention to provide a process for the fractionation of mixtures comprising straight-chain organic compounds having varying degrees of unsaturation. It is another object of the present invention to provide a process for the separation of mixtures of organic compounds into fractions having relatively more and less a degree of unsaturation. ,It is an additional object of this invention to provide a process for the improvement of vegetable oil acids for use in coating compositions. Other objects will become apparent during the following discussion.

This invention is based upon the discovery that mixtures of straight-chain polar organic compounds may be effectively separated into fractions respectively richer and poorer in the chemically less saturated components by clathrate compound formation with urea.

In accordance with this invention, a mixture of straight-chain polar organic compounds containing components having varying degrees of chemical unsaturation has urea admixed therewith, as more fully described hereinafter. The relatively more saturated components form crystalline clathrate compounds with urea, while the relatively less saturated components remain unchanged.

It has been found, still in accordance with the present invention, that mixtures of fatty acids may be fractionated by the preferential formation of crystalline clathrate compounds between urea and acids having relatively low unsaturation. Still in accordance with this invention, it has been found that th potential drying characteristics of vegetable-and-animal-oil acids may be substantially improved by treatment of such mixtures of acids with urea so as to extract the acids having a low degree of unsaturation, i. e., less than two double bonds, thus leaving as a rafiinate the more unsaturated members having the best potential drying characteristics.

The process of the present invention may be applied with equal or even greater effectiveness to the mixtures of esters of the above acids, especially when the esters are formed by esterification with a straight-chain monohydric alcohol. It may also be applied to fatty alcohols comprising mixtures of varied degrees of unsaturation. Branched-chain or cyclic compounds will not usually form clathrate compounds with urea of the type described.

Th term clathrate compounds has been coined recently as a generic name for molecular complexes such as those formed by urea, as described hereinafter. While the formation of clathrate compounds of urea and straight-chain hydrocarbons had been discovered, no adequate explanation was available of how the two molecules were united in the absenc of chemical reaction. In the investigations from which the present invention resulted, X-ray and crystallographic studies have elucidated the structure to adequately explain the topography of the complex molecules and to describe the types of materials which undergo clathrat formation with urea.

A paper by H. M. Powell, J. Chem. Soc. (1948), 61-73, describes, in general, the theory behind the formation of clathrate compounds. Powell defines these as follows:

A structural combination of two substances which remain associated, not through strong attraction between them, but because strong mutual binding of the molecules of one sort only mak s possible the firm enclosure of the other.

As stated hereinbefore, crystallographic and X-ray examinations of the clathrate compounds with which the present invention is concerned were necessary to explain the phenomenon involved. It has been found that th clathrate compounds comprise spiral-like arrangements of urea molecules which bind within the spiral a second organic compound. The X-ray data have shown that urea apparently forms a spiral having a critical inner diameter and that this diameter does not appreciably vary with conditions such as temperature or environment. In order to form a clathrate compound therewith, an organic substance must have an unbranched configuration except for terminal atoms. Th crosssectional diameter of a straight-chain organic 3 7 compound primarily depends upon bond angles between carbon atoms or other atoms comprising the straight chain and upon the diameter of substituent groups or atoms attached to the chain.

The critical requirements described above permit the use of clathrate formation from the fractionation of mixtures of polar organic compounds. Branched-chain compounds, for example, have cross-sectional diameters larger than that which will permit the compound to fit into the urea spiral. Hence, these substances do not undergo clathrate formation with urea. Straight-chain organic compounds form clathrates with urea with increasing reluctance as their degree of unsaturation increases.

These considerations have led to the invention of the present process for the fractionation of mixtures of the acids derived from naturally occurring fats and oils. In order to take advantage of the present process, it has been found necessary to hydrolyze the mixtures of naturallyoocurring glycerides in order to leave the free acids or their esters of monohydric straightchain alcohols or to otherwise destroy the branching caused by the glyceryl radical of an oil. The methods of hydrolysis, ester interchange and reduction used for these purposes are well known in the art. Preferably, when esters are to be employed, the lower aliphatic alcohols such as methyl, ethyl, amyl, etc., are employed. While the treatment of the mixtures of free acids gives sufficient fractionation for most purposes, it has'been found that the use of the lower esters such as the methyl esters allows a greater degree of fractionation at ordinary temperatures.

Typical vegetable oils containing acids which may be treated in this way include soybean, cottonseed, linseed, cocoanut, perilla and hemp seed oils, as well as oiticica and tung oils. Fish oils such as sardine, menhaden, Whale oil and fish liver oils also provide suitable acids for use in the present process. Other sources comprise tall oil, isomerized linseed and soybean oils, as well as dehydrated castor oil. While the process of the present invention may be employed in the fractionation of other mixtures, as described hereinafter, it will be described with particular reference to acids obtained from the above typical sources.

Linseed oil comprises primarily a mixture of glycerides of fatty acids having a typical analysis as follows:

Per- Iodine Acid cent No.

Stearic and Palmitic 15 O1eic. 13 90 Linoleic 17 181 Linolenic. 54 273 Arachidic l usually react. Similarly, with increasing reaction temperature, the compounds having a relatively greater degree of unsaturation from clathrate compounds with urea with increasing reluctance. Conversely, a larger fraction of any of the above mixtures may be isolated by the use of relatively low temperatures, that is, below about 35 C. Hence, it becomes possible to employ a temperature gradient so as to separate a specific mixture into a number of desired fractions. This is especially important when particular species or narrow cuts according to molecular weight or degree of unsaturation are required.

The mixtureof fatty acids may be treated in the absence of any diluent or solvent; however, it is usually preferable to include a diluent such as a ketone or alcohol. Suitable diluents include especially methyl isobutyl ketone and methyl ethyl ketone. Alcohols which are preferred include those having four and five carbon atoms and may be primary, secondary or tertiary in structure. Mixtures of such solvents may be employed. The use of equal amounts of amyl alcohols with methyl isobutyl ketone has been found especially useful for the subject process. This particular type of mixture permits rapid separation of the raffinate from the crystalline clathrate compounds. The term rafilnate is used in the present case to describe the unaffected fractions of the mixtures treated with urea.

The use of solvent-to-fatty acid ratios of at least 2:1 to about 4:1 has been found to promote the most favorable conditions for clathrate formation. Ratios within this range favor the formation of large crystals which separate cleanly from the raflinate and hence favor the formation of pure fractions.

Urea may be dissolved in a suitable solvent or may be employed in the crystalline state. Preferably, it is dispersed in an aqueous medium and, still more preferably, is employed as a solution which is initially saturated at the temperature of the reaction. The concentration of urea in its solvent may be adjusted to. obtain selective fractionation, since it has been found that solutions having less than a saturation content of urea have a diminished reactivity with some components of the mixtures treated.

The ratio of urea to the mixture of organic compounds is an additional factor which may be varied in controlling the degree and type of the resulting fraction. The examples which follow principally show the use of equal molar amounts of urea and vegetable oil. As the amount of urea with relation to the vegetable oil acids is reduced, the process becomes increasingly selective. Since the clathrate compounds being considered normally comprise one mol of urea for each carbon atom in the extracted component, the molar ratio of urea to the active fraction of the vegetable oil should be quite large. Even under the most favorable conditions, it is a preferred practice to employ a large excess of urea when a maximum removal is desired. However, a reduced quantity of urea may be employed in controlling the removal of specific fractions.

The process generally comprises mixing the fatty acids with urea in a reactor column by means of rapid stirring, allowing the mixture to remain in the reactor for a time sufficient for complete reaction and then transporting the reacted mixture to a separator. The separator may comprise a settling tank, filter or centrifuge,

depending upon the exact character of the mixture and the ease with which it may be separated by any one of these means. If a settling tank is employed, the raffinate separates from the crystalline clathrate compounds and the residual urea solution. After removal of the railinate, the mixture of dilute urea solution and clathrate compounds may be heated to a temperature' of 80-125 0., in order to decompose the clathrate and regenerate both fatty acids and urea therefrom. A convenient process step comprises permitting decomposition to take place in the presence of the dilute urea solution, whereupon the regenerated urea redissolves in the urea solution and is recirculated for additional fractionations.

It has been discovered, in accordance with the present invention, that the process described permits the concentration of highly unsaturated acids and the less unsaturated acids into at least two separate fractions. As the degree of unsaturation diminishes, the tendency to form clathrate compounds with urea increases. Data from which these statements are based will be found in the examples given hereinafter.

If centrifuging or filtration are employed as the means of separation, the crystalline clathrate compounds are separated from the liquid components of the mixture, namely, the dilute urea solution and the rafinate fraction. The clathrate compounds may be regenerated by the use of heat or by such methods as steam distillation or treatment with hot organic solvents or water.

It has been noted that urea solutions tend to promote rapid corrosion of iron equipment and even of fixtures composed of cement. This appears to be caused by oxidation, which apparently is accelerated in the presence of urea. The equipment may be protected by blanketing with an inert gas, such as nitrogen, by including corrosion inhibitors in the mixture, such as ammonium phosphate and ammonium chromate, or by coating the equipment with resins or corrosion-resistant metals.

While the process of the present invention has been described particularly with reference to mixtures of naturally-occurring acids, the phenomena involved permit its application to the fractionation of other mixtures containing straight-chain components of varying degrees of saturation bearing a common polar group throughout. Hence, it is possible to fractionate mixtures of amines, amides, nitriles, esters, alcohols, aldehydes or ketones having components of varying degrees of saturation.

Particular species of fatty acids which readily form clathrate compounds include especially the saturated straight-chain fatty acids having four to fifty carbon atoms, such as butyric, caprylic, myristic and stearic acids and the ,mono-olefinic acids such as oleic acid. Unsaturated fatty acids which form clathrate compoundswith urea. with some reluctance under the conditions described include especially linolenic and elaeostearic acids; specific esters which readily form clathrate compounds with urea are methyl stearate and ethyl palmitate.

The following examples illustrate the process of the present invention.

Two-hundred and fifty parts by weight of each of the fatty acid mixtures described hereinafter were diluted with an equal amount ofmethyl isobutyl ketone. The dilute mixturewas stirred with 2000 parts by weight of saturated aqueous. urea solution at 22-25 C. In the course of five min- 6 utes, a white crystalline precipitate formed, which was separated by filtration and washed with 500 parts of methyl isobutyl ketone. The precipitate, which was the mixture of clathrate compounds, was decomposed by stirring in 1000 parts by weight of water at C. The oily layer which formed was separated from the aqueous layer which contained regenerated urea. Methyl isobutyl ketone was removed from the oily layer by distillation to 110 C. at 0.5 mm. mercury pressure. The railinate was recovered as an oily layer from the dilute urea solution obtained in the original filtration. Methyl isobutyl ketone was removed therefrom as described above. The iodine values of the fatty acids, regenerated from the clathrate compounds and of the rafiinate were determined and are reported below. Methyl esters of each of the three types of fatty acid mixtures were treated in a similar manner. The results obtained are given in the table which follows.

Iodine Examples ig g n eag ngma g. g. Weight Wills l. Linseed Fatty Acids 250 100 180 Extract 49 i9. 6 54 Raflinate 201 80. 4 a 199 2. Soybean Fatty 250 100 138 Extract 38 15. 2 59 Rallinate 212 84. 8 146 3. Dehydrated Castor Oil:

Fatty Acids. 250 100 1 167 Extract 25 10 1 107 225 1 170 F Acid 250 100 139 Extract 112 44.7 97 Raifinate 138 55. 3 175 6. Methyl Ester of Dehydrated:

C stor Oil Fatty Acids 250 100 1 162 Extract 125 60 1 Raffinate 125 50 1 174 Woburn Iodine Values. For method see Ind. Eng. Chem., anal. ed., vol. 13, pg. 782, November 15. 1941.

EXAMPLE? Urea extraction of the alcohols obtained from the reduction of linseed oil.

Linseed oil acids were reduced to the unsaturated straight-chain alcohols by use of metallic sodium and methyl isobutyl carbinol (Ind. Eng. Chem. 39 55-62 (1947) This reduction retains the unsaturation present in the linseed acids. The distilled alcohols boiling between l64182 C. at 0.8-1.7 mm. were used in the following ex-- traction.

Two-hundred and fifty grams of the alcohols were mixed with 250 grams of methyl isobutyl ketone and poured into 2000 m1. .of saturated urea solution at 25 C. After fifteen minutes, a precipitate began to form. The mixture was stirred for forty-five minutes longer and then filtered. The precipitate was carefully washed with 500 ml. of methyl isobutyl ketone. The washed precipitate Was decomposed in one liter of water at 80 C. The upper oily layer which separated was washed, filtered and the remaining methyl isobutyl ketone removed under vacuum. Weight of extract, 71 g.

The railinate in the methyl isobtuyl ketone was washed, filtered and the methyl isobutyl ketone removed under vacuum. Weight of raffinate, 158 g.

Analysis. of products The extract was a mushy solid at room temperature, while the starting alcohol and rafiinate were both mobile liquids.

f EXAMPLE 3 Urea extraction of tall oil The tall oil used in this. extraction had an analysis as follows: 7

Two-hundred and fifty grams of tall oil were dissolved in 250 g. of methyl isobutyl ketone and stirred into 200 ml. of saturated urea solution at 25 C. The mixture was stirred forty-five minutes, while a large amount of precipitate formed. This was filtered on and carefully washed with methyl isobutyl ketone. The precipitate was de- Analysis of products Starting Methyl Extract Raflinate Esters Weight, 200 44 140 Iodine Number 141 77. 8 160 Refractive Index, Nn 1. 4575 1. 4508 1. 4601 EXAMPLE 10 Urea extraction of a mixture of stearic and oleic acid Thisexperiment was run to determine whether stearic acid could be separated from oleic acid by urea extraction. Oleic acid, 150 g., stearic acid, 50 g., and methyl isobutyl ketone 200 g. were mixed. This clear solution was stirred with 200 ml. of saturated aqueous urea solution at 25 C. The crystalline complex which formed was filtered off, washed with methyl isobutyl ketone, and decomposed with warm water. The product which separated was a hard solid at room temperature. It was dissolved in toluene, washed with water, and all solvent removed under vacuum. This was designated #1. The methyl isobutyl ketone solution of the mixture that did not form a complex was washed with water, and another 200 ml. of saturated aqueous urea added. The product separated was designated $2. This was repeated until five extractions had been made. The rafiinate was then worked up by washing it in the methyl isobutyl ketone solution. and then evaporating the methyl isobutyl ketone composed in one liter of water at 80 C. The under Vacuumupper layer which formed was separated, washed, Analytical s s and the solvent evaporated under vacuum. Weight of extract, 31 g. V Wijs V The raffinate was recovered by separating the Weight bigcninjgr upper oily layer from the dilute'urea solution fil- 40 trate, and washing and evaporating the solvent 8 17' (5) from the oil. Weight of raffinate, 208 g. 10 26. 7) Analysis of products were as follows: 2 #5 s 27. o) Raffinate 116 84. (3) Stafl'n-1g Extract Rafiinate Mating EXAMPLE 11 e -1 250 31 208 Urea extraction of a fraction of methyl linseedate li tiitt t.H t haiaat1 (23 having a high iodine value The following experiment was run to determine The extract was a very light-colored, waxy solid. 7

EXAMPLE 9 Urea extraction of the methyl esters of soybean acids using no solvent for the area The methyl esters of soybean fatty acids were made from refined soybean oil by exchange with methanol, B. P. 138-148 at 0.2 to 0.5 mm. mercury pressure. Two-hundred grams of the methyl esters were poured into a small ball mill and 100 g. of solid urea were added. The contents were milled overnight. To work up the mushy mixture that resulted, methyl isobutyl ketone was added, and the crystals were filtered off. The crystals were washed with more methyl isobutyl ketone and then decomposed with warm water. The upper layer, which separated, was Washed, and the remaining solvent evaporated under vacuum. Weight of extract, 44 g. The raflinate in the methyl isobutyl ketone was washed, and the solvent taken off under reduced pressure. Weight of raffinate, 140 g.

if a urea complex could be formed from a fraction of methyl esters of linseed oil acids that had two or more double bonds per molecule. The rafiinate from the urea extraction of methyl linseedate (Example 4) was used in this experiment. The iodine value was 224, indicating that the fraction was predominately the ester of linoleic acid (iodine value, 172.8) and linolenic acid (iodine value, 261.3)

Fifty grams of this rafiinate were diluted with an equal weight of methyl isobutyl ketone and shaken with 900 ml. of saturated aqueous urea at 25 C. After shaking four hours, a crystalline complex started to form,and the shaking was continued for twenty-four hours. The precipitate was carefully filtered ofi and washed with methyl isobutyl ketone. It was decomposed in warm water, and the upper layer was washed with water, and all solvent evaporated. Weight of extract, 21 g.; idodine value, 217

The rafi'inate in the methyl isobutyl ketone solution was washed with water, and the solvent removed under vacuum. Weight of rafiinate,

24 g.; iodine value, 231.

EXAMPLE 12 Ur xt a ti n f he et yl esters of s l/ e fatty acids 7 The ethyl, esters of soybean fatty acids were prepared from refined so b an oi y exchange with ethanolwc undred r ms o h esters were mixed with twoehundred. ams. o m h isobutyl heton and stirred with t o t s of saturated aqu ou use at C- A cr s n complex readily formed, and the stirring was continued for one-half hour. The precipitated complex was filtered o f. w sh d with t y isobutyl k ton and; d c m osed w r t The, upper layer which, sepfl jated was washed with wat r, sepa ated, and t e s nt removed under vacuum- Wei ht of e t ct, 57 g- The. raflinate n h meth s utrl k t n s uti n was. washed wi h wa er separ ted an h solvent r mo ed under a uum- We o a nata. 2:7

Analysis of product Urea, extraction 0) the methyl esters of soybean fatty acids using no solvents for the esters or urea re-hundre rams 9 the me y esters of scrbe n fatty ids we e m x d wi 300 f finel -around u e e mi t e s stirred for six hours in a beaker blanketed with carbon dioxide. The mixture was then poured into the basket of a centrifugal filter, and the ramnate spun away from the crystalline complex that had formed.

The crystalline complex was stirred in 1500 m1. of warm Water. Th upper layer which separated was washed with water and dried by filtering through paper. Weight of extract, 50 g.; Wijs iodine value,-73,9.

The rafiinate as it came from centrifuge was clear and was analyzed without further treatent. Weight of raflinate, 401 g.; iodine value, 148.

EXAM LE 14 Urea extraction of the methyl esters of tung oil fatty acid Analysis of products Starting Material Extract Railinaic W ht, 259 54 186 Wonurn lodu c Number 1 21 0 i 179 230 1b Ind. Eng. Chem Ans]. Ed, vol. page 782,Novombcr i5,

-;We c a ms-s ourin ent na the Processfcr the fractionatio ,of mixtu s of fatty acids of dif er ng de -Ices of t t ration resulting from the hydrolysis of vegetable oils the steps which comprises contacting said mixture at 0-755 C. with an aqueous solution of urea, whereby crystalline clathrate compounds of urea and the relatively less unsaturated or saturated components thereof are formed but the relatively more unsaturated acids are unaffected, and separating said clathrate compounds from the relatively more unsaturated acids.

2. In a process for the improvement in drying properties of vegetable oils, the process which comprises subjecting said oils to hydrolysis, whereby the glycerides present in the oils are hydrolysed to form a mixture. of fatty acids having varying degrees of saturation; treating said mixture with urea'at a temperature of 0-75 0., whereby the clathrate compounds form between urea and the acids having the relatively greater degree of saturation, the unaffected raflinate comprising the acids which have a relatively greater degree of unsaturation.

3. In a process for the fractionation of a mixture comprising esters of fatty acids of differing degrees of saturation resulting from the hydrolysis of vegetable oils and lower monohydric alcohols the steps which comprise contacting said mixture with an aqueous solution of urea at a temperature of 0-75 0., whereby crystalline clathrate compounds of urea and esters having relatively less unsaturation or saturation are formed while esters having relatively more unsaturation are unaffected, and subsequently separating the clathrate compounds from the unaffected esters.

4. In a process for the fractionation of a mixture of straight-chain polar organic compounds bearing an unbranched hydrocarbon chain, a fraction A of which comprises chemically less unsaturated or saturated straight-chain polar organic compounds bearing an unbranched hydrocarbon chain and a fraction B of which comprises chemically more unsaturated straightchain polar organic compounds bearing an unbranched hydrocarbon chain bearing a polar substituent of the same chemical class as that borne by the compounds of fraction A, the steps which comprise contacting urea with said mixture at a temperature between 0-'75 0., whereby the compounds of fraction A form crystalline molecular complexes with urea but fraction B is unaffected, and separating said molecular complexes from fraction B.

5. A process for the separation of mixtures of straight-chain polar organic compounds bearing an unbranched hydrocarbon chain having differing degrees of unsaturation comprising contacting said mixture at a temperature of 0-? 5 C. with urea whereby crystalline complexes are formed between urea and a fraction A of said mixture, a fraction B of said mixture being inert towards urea under the contacting conditions, separating the resulting crystalline complexes from said fraction B, and regenerating polar compounds of fraction A from the separated complexes, fraction A being enriched in relatively less unsaturated straight-chain polarorganic compounds bearing an unbranched hydrocarbon chain and fraction B being enriched in relatively more unsaturated straight-chain polar organic compounds bearing an unbranched hydrocarbon chain bearing a polar substituent of the same chemical classes that borne by the compounds of fraction A.

6. A process according to claim 1 wherein the vegetable oil is soybean oil.

7. In a process for the fractionation of a mixture of polar organic compounds selected from the group consisting of mixtures of long-chain fatty acids, mixtures of esters thereof with monohydric alcohols, and mixtures of long-chainfatty alcohols, a fraction A of which mixture comprises chemically less unsaturated or saturated straight-chain polar organic compounds and a fraction B of which comprises chemically more unsaturated straight-chain polar organic compounds bearing a polar substituent of the same chemical class as that borne by the compounds of fraction A, the steps which comprise contacting urea with said mixture at a temperature between and 75 C. whereby a first portion enriched in the compounds of fraction A form crystalline clathrate compounds with urea but a second portion enriched in compounds of fraction B is unaffected and separating said clathrate compounds from said second portion.

8. In the process for the fractionation of mixtures of fatty acids of differing degrees of saturation and having from 4 to 50 carbon atoms, the steps which comprise contacting said mixture at a temperature between 0 and 75 C. with an aqueous solution of urea whereby crystalline molecular complexes of urea and a first portion enriched in the relatively less unsaturated or saturated straight-chain components thereof are formed but a second portion enriched in the relatively more unsaturated straight-chain acids is unafiected and separating said molecular complexes from said second portion.

9. In the process for the fractionation of mixtures of fatty alcohols of differing degrees of saturation, the steps which comprise contacting said mixture at a temperature between 0 and 75 C. with an aqueous solution of urea whereby crystalline molecular complexes of urea and a first portion enriched in the relatively less unsaturated or saturated straight-chain components thereof are formed but a second portion enriched in the relatively more unsaturated straight-chain acids is unaffected and separating said molecular complexes from said second portion.

10. In the process for the fractionation of mixtures of fatty esters of substantially unbranched fatty acids and monohydric alcohols of differing degrees of saturation, the steps which comprise contacting said mixture at a temperature between 0 and 75 C. with an aqueous solution of urea whereby crystalline molecular complexes of urea and a first portion enriched in the relatively less unsaturated or saturated straight-chain components thereof are formed but a second portion enriched in the relatively more unsaturated straight-chain acids are unaffected and separating said molecular complexes from said second portion.

11. A process for the fractionation of mixtures of fish oil fatty acids having differing degrees of saturation comprising contacting said mixture at a temperature of 0-75 C. with urea, whereby crystalline complexes are formed between urea and a fraction A of said mixture, a fraction B of said mixture being inert toward urea under the contacting conditions, separating the resulting crystalline complexes from said fraction B and regenerating fatty acids from the separated complexes, fraction A being enriched in relatively less unsaturated fatty acids and fraction B being enriched in relatively more unsaturated fatty acids.

12. In a process for the fractionation of a mixture of polar organic compounds selected from the group consisting of mixtures of long chain fatty acids, mixtures of esters thereof with monohydric alcohols and mixtures of long chain fatty alcohols, a fraction A of which mixture comprises chemically saturated or less unsaturated straight-- chain polar organic compounds and a fraction B- of which comprises chemically more unsaturated straight-chain polar organic compounds bearing a polar substituent of the same chemical class as that borne by the class of compounds of fraction A, the step which comprises contacting urea with said mixture at a temperature between 0 and 75 C. whereby a first portion enriched in the compounds of fraction A form crystalline molecular complexes with urea but a second portion 7 enriched in compounds of fraction B and containing some less unsaturated compounds of fraction A is substantially unaffected under the conditions of contact; separating said crystalline molecular complexes from said second portion and subsequently contacting said second portion with an additional quantity of,urea whereby a relatively less unsaturated fraction thereof forms crystalline molecular complexes with urea.

13. In the process for the fractionation of mixtures of straight-chain polar organic compounds bearing an unbranched hydrocarbon chain, a fraction A of which mixture comprises compounds having a relatively lesser proportion of olefinic linkages and a fraction B of which comprises compounds having a relatively greater proportion of olefinic linkages and bearing a polar substituent of the same chemical class as that borne by the compounds of fraction A, the steps which comprise contacting urea with said mixture at a temperature between 0 and 75 C. whereby afirst portion enriched in the compounds of fraction A form crystalline molecular complexes with urea but a second portion enriched in compounds of fraction B is unaffected, and separating said molecular complexes from said second portion.

14. In the process for the fractionation of mixtures of long-chain fatty acids of differing degrees of saturation, the steps which comprise contacting said mixture at 0-75 C. with urea, whereby crystalline molecular complexes of urea and saturated or relatively less unsaturated straight-chain components thereof are formed but the relatively more unsaturated straightchain acids are unaffected, and separating said molecular complexes from the relatively more unsaturated acids.

15. In a process for the fractionation of a mixture of polar organic compounds selected from the group consisting of mixtures of long-chain fatty acids, mixtures of esters thereof with monohydric alcohols, and mixtures of long-chain fatty alcohols, a fraction A of which mixture cornprises chemically saturated or less unsaturated straight-chain polar organic compounds and a fraction B of which comprises chemically more unsaturated straight-chain polar organic compounds bearing a polar substituent of the same chemical class as that borne by the compounds of fraction A, said mixture being dissolved in a substantially inert solvent with respect to urea, the steps which comprise contacting urea with said. mixture at a temperature between 0 and 75 C. whereby a first portion enriched in compounds of fraction A form crystalline molecular complexes with urea but a second portion enriched in compounds of fraction B is unaffected and separating said molecular complexes from saidsecond por- 16. In a process for the fractionation of a mix- 17. A process according to claim 1 wherein the ture of polar organic compounds selected from vegetable oil is tall oil. the group consisting of mixtures of long-chain HERBERT A. NEWEY. fatty acids, mixtures of esters thereof with mono- EDWARD C. SHOKAL. hydric alcohols, and mixtures of long-chain fatty THEODORE F. BRADLEY. alcohols, a fraction A of which mixture comprises chemically saturated or less unsaturated straight- REFERENCES CITED chain polar organic compounds and a fraction B Th f 11 f f th of which comprises chemically more unsaturated e o .owmg memes ale ream m e straight-chain polar organic compounds bearing me of thls patent a polar substituent of the same chemical class as UNITED S A S PATEN that borne by the compounds of fraction A, said Number Name Date mixture being dissolved in a substantially inert 2,520,715 Fetterly 29 1950 solvent, the steps which comprise contacting fine- 1y ground urea with said mixture at a tempera- OTHER REFERENCES ture between 0 and C. whereby a first portion Reel 143, Technical Oil Missions, translated by enriched in compounds of fraction A form crystal- Shell 00., deposited in Library of Congress,

line molecular complexes with urea but a second May 22, 1946, pages -139. portion enriched in compounds of fraction B is unaffected, and separating said molecular com- 20 plexes from said second portion. 

13. IN THE PROCESS FOR THE FRACTIONATION OF MIXTURES OF STRAIGHT-CHAIN POLAR ORGANIC COMPOUNDS BEARING AN UNBRANCHED HYDROCARBON CHAIN, A FRACTION A OF WHICH MIXTURE COMPRISES COMPOUNDS HAVING A RELATIVELY LESSER PROPORTION OF OLEFINIC LINKAGES AND A FRACTION B OF WHICH COMPRISES COMPOUNDS HAVING A RELATIVELY GREATER PROPORTION OF OLEFINIC LINKAGES AND BEARING A POLAR SUBSTITUENT OF THE SAME CHEMICAL CLASS AS THAT BORNE BY THE COMPOUNDS OF FRACTION A, THE STEPS WHICH COMPRISE CONTACTING UREA WITH SAID MIXTURE AT A TEMPERATURE BETWEEN 0* AND 75* C. WHEREBY A FIRST PORTION ENRICHED IN THE COMPOUNDS OF FRACTION A FORM CRYSTALLINE MOLECULAR COMPLXES WITH UREA BUT A SECOND PORTION ENRICHED IN COMPOUNDS OF FRACTION B IS UNAFFECTED, AND SEPARATING SAID MOLECULAR COMPLEXES FROM SAID SECOND PORTION. 